This invention relates to high frequency cavities and waveguides having surfaces in contact with the radiation made of high temperature superconducting materials.
Recently, high temperature superconducting ceramic materials have been discovered whose transition to the superconducting state occurs at temperatures above 35.degree.K. These high temperature superconducting ceramic materials include rare earth elements such as yttrium, lanthanum, and europium combined with barium and copper oxides. A representative high temperature superconducting material is the Y-Ba-Cu-O system. See, J.G. Bednorz and K.A. Muller, Z. Phys., B 64, 189 (1986) and M.K. Wu, J.R. Ashburn, C.J. Torng, P.A. Hor, R.L. Meng, Z.J. Huang, Y.Q. Wang, and C.W. Chu, Phys. Rev. Lett. 908 (1987). These materials have critical temperatures of up to approximately 90.degree.K or above.
Because ohmic power losses can be a major limitation in microwave/far infrared technologies, it would be advantageous to use superconducting materials for cavities and waveguides. Although conventional, low temperature superconducting materials have been used to reduce greatly these ohmic losses in ultrahigh Q cavities at microwave frequencies, there are significant constraints due to operation at liquid helium temperatures. Moreover, photons in the millimeter-wave/far infrared range can cause transitions across the superconducting energy gap, thereby removing the superconducting properties. There are also limitations due to thermal excitations across the gap. For these reasons, conventional superconductors have not been employed for gyrotron cavities, mode converters, accelerators and free electron lasers, and waveguides operating at wavelengths less than approximately one centimeter.